1. Field
The present invention relates to a refrigerant cycle device, and more particularly to a refrigerant cycle device in which carbon dioxide is used as a refrigerant.
2. Description of the Related Art
A conventional refrigerant cycle device includes a refrigerant cycle configured such that a compressor, a gas cooler, a pressure reducing device (e.g., expansion valve) and an evaporator are sequentially pipe-connected to each other in a closed loop.
Freon (R11, R12, R134a, etc.) has been commonly used as a refrigerant of a refrigerant cycle device. However, because freon discharged in the atmosphere causes problems of global warming, disruption of the ozone layer and the like, there has been research related to the use of a natural refrigerant having little influence on the environment, e.g., oxygen (O2), carbon dioxide (CO2), hydrocarbon (HC), ammonia (NH3), or water (H2O) as a refrigerant.
Of the above natural refrigerants, because oxygen and water have low pressure, it is difficult to use these compounds as a refrigerant. Because ammonia and hydrocarbon are combustible, these materials are difficult to handle. Accordingly, there is being developed a device using a transcritical cycle in which carbon dioxide (CO2) is used as a refrigerant and a high pressure side is set to a supercritical pressure.
A transcritical cycle device is constituted such that an accumulator is mounted to a low pressure side between an outlet of an evaporator and a suction port of a compressor to prevent inflow of a liquid refrigerant into the compressor, and the liquid refrigerant is accumulated in the accumulator, so that only a gas refrigerant is sucked into the compressor.
However, the conventional refrigerant cycle device has problems such that the charging amount of refrigerant is increased due to the installation of the accumulator and the refrigerant cycle device cannot be made compact.
To solve the above problems, Korean Patent Laid-Open Publication No. 2006-0041722 discloses a refrigerant cycle device capable of preventing damage to a compressor due to liquid compression without installing an accumulator.
The above-disclosed refrigerant cycle device is a transcritical cycle device in which a compressor, a gas cooler, a pressure reducing device and an evaporator are connected to each other in a closed loop, carbon dioxide is used as a refrigerant, and a high pressure side is set to a supercritical pressure. The disclosed refrigerant cycle device includes an internal heat exchanger to heat-exchange a refrigerant discharged from the gas cooler and a refrigerant discharged from the evaporator. The internal heat exchanger includes a high pressure side passage through which the refrigerant discharged from the gas cooler flows, and a low pressure side passage through which the refrigerant discharged from the evaporator flows. The high pressure side passage and the low pressure side passage are arranged so as to be heat-exchanged with each other. The refrigerant in the high pressure side passage flows from down to up, and the refrigerant in the low pressure side passage flows from up to down.
By making the refrigerant in the high pressure side passage flow from down to up and the refrigerant in the low pressure side passage flow from up to down, a surplus refrigerant is accumulated in the high pressure side passage, and the amount of surplus refrigerant flowing into the low pressure side passage is reduced. Accordingly, the above-disclosed refrigerant cycle device shows an effect of preventing inflow of a liquid refrigerant into the compressor to a certain extent. However, if a large amount of surplus liquid refrigerant is included in the refrigerant flowing through the evaporator because a temperature around the evaporator is low, the inflow of the liquid refrigerant into the compressor cannot be perfectly prevented by the constitution such that the refrigerant from the evaporator flows from up to down in the low pressure side passage.
Also because the refrigerant in the high pressure side passage flows from down to up, the liquid refrigerant flowing to the expansion valve is evaporated, and flash gas is generated, which causes deterioration of the performance of the expansion valve.
Further, because a first refrigerant pipe and a second refrigerant pipe of the internal heat exchanger are spaced apart from each other, when the refrigerant flows through the internal heat exchanger or when vibration by the operation of the compressor is transmitted, the first refrigerant pipe of the internal heat exchanger vibrates to be contacted with the second refrigerant pipe, thereby generating noise. If the first and second refrigerant pipes get worn by the successive contact, operational reliability of the refrigerant cycle device is deteriorated.
Still further, when a temperature of the refrigerant at the outlet of the evaporator rises, a heat exchange area of the internal heat exchanger should be increased in order to achieve a sufficient heat exchange effect. To fulfill such a requirement, a length of the double pipe type internal heat exchanger should be increased, which results in increase in cost of the internal heat exchanger. There is also a limitation in improving the performance of the refrigeration cycle due to the insufficient heat exchange.